A head mount type image display system is roughly broken down into two usage patterns: one where the user watches fixedly (without moving the body largely) at only electronic images displayed by the head mount type image display system while the field of outside view is cut off as much as possible, and another where the head mount type image display system is used for the purposes of checking the necessary information upon working operation, checking emergent information out of doors, etc.; the user views electronic images while, at the same time, the field of outside view is ensured as much as possible. And then, the head mount type image display system that is going to be used according to the latter usage pattern has a mechanism called a see-around or see-through mechanism for the purpose of making sure the field of outside view. The present invention is concerned with a head mount type image display system that is going to be used according to the latter usage pattern and so has the see-around or see-through mechanism.
The see-around mechanism is to enable the user to view outside images around an electronic image significantly in an unobstructed way, even when the head mount type image display system remains mounted on the user's head. Typical prior arts are Patent Publications 1, 2 and 3.
On the other hand, the see-through mechanism is to make it possible for the user to view outside images while they overlap electronic images displayed by the head mount type image display system. Typical prior arts are Patent Publications 4, 5 and 6.                [Patent Publication 1] JP(A)8-166557        [Patent Publication 2] JP Domestic Publication No. 2003-502713        [Patent Publication 3] U.S. Pat. No. 3,923,370        [Patent Publication 4] U.S. Pat. No. 5,646,784        [Patent Publication 5] 2000-196975        [Patent Publication 6] JP(A)10-301055        [Patent Publication 7] JP(A)8-313829        [Patent Publication 8] JP(A)11-249067        